Abstract

The Great Australia deposit, near Cloncurry, Queensland, Australia, hosts an unusual enrichment in the copper nitrate mineral gerhardtite. Nitrogen isotope analyses suggest that oxidized ammonia from nearby termite mounds provides the nitrate required for gerhardtite mineralization. Groundwater δ15N and [NO3−] show a correlated decrease with depth, suggesting a surface source of nitrogen, with δ15NAIR > +10‰. The δ15N values of gerhardtite (δ15NAIR = +13.3‰) and local bulk termite-mound material (δ15NAIR = +13.5‰) are virtually identical, and the remote desert location of the deposit precludes a septic or manure source of nitrogen. Similarly, remobilization of older inorganic evaporitic nitrates is an unlikely source owing to both geology and climate. Field evidence suggests that the spatial distribution of termite mounds may be a useful predictor of base-metal speciation as nitrates within the oxidation zone of base-metal deposits.